critical CVSS 10 EPSS 0.24%

CVE-2026-54763·Traefik vulnerability

Traefik is an HTTP reverse proxy and load balancer. Prior to v2.11.51, v3.6.22, and v3.7.6, Traefik's BasicAuth, DigestAuth, and ForwardAuth middlewares strip canonical-cased spoofed identity headers before writing Traefik's own value, but do not account for underscore-variant header names, which many backends normalize identically to dashed forms. An attacker able to reach a protected route can inject an underscore-variant header that survives Traefik's stripping and reaches the backend alongside, or on the unauthenticated ForwardAuth authResponseHeaders path instead of, the value Traefik intended to set, spoofing identity or authorization context. This issue is fixed in versions v2.11.51, v3.6.22, and v3.7.6.

Severity
critical
Software
Traefik
Fixed in
3.7.6
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.24% — higher than 14% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-54763 scores 10 on CVSS, so a successful attack would be serious — but at 0.24%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 3.7.0

Until: 3.7.6

Fixed in: 3.7.6

How to fix this CVE

Upgrade Traefik immediately to version 3.7.6 or later to patch header injection vulnerabilities in authentication middlewares. The vulnerability allows attackers to bypass identity verification by injecting underscore-variant HTTP headers that evade Traefik's sanitization logic. Ensure all reverse proxy instances are updated and restarted to apply the security fix.

sudo dnf update traefik

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET|POST|PUT|DELETE .* HTTP/1\.1.*\n(.*\n)*(authorization|x_forwarded_user|remote_user|x_remote_user|cookie): .*

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Block or normalize HTTP headers containing underscore-variant names before routing to backend services. Implement header canonicalization rules to convert underscore-prefixed headers to dashed equivalents and reject requests with both variants present simultaneously.

How to check if you are affected

  1. Step 1: Check installed Traefik version with: traefik version or docker inspect $(docker ps -q -f 'ancestor=traefik') | grep -i version
  2. Step 2: Verify if BasicAuth, DigestAuth, or ForwardAuth middleware is enabled in traefik.yml or dynamic configuration by grepping for 'basicAuth\|digestAuth\|forwardAuth'
  3. Step 3: Search access logs for requests containing underscore-prefixed header variants (e.g., 'authorization', 'x_forwarded_user', 'remote_user') that don't match canonical dashed versions
  4. Step 4: After patching, confirm version shows v3.7.6 or higher and restart with: sudo systemctl restart traefik or docker-compose restart traefik

FAQ

What is CVE-2026-54763?

CVE-2026-54763 is a header injection vulnerability in Traefik's authentication middlewares where underscore-variant HTTP header names bypass security filtering, allowing attackers to spoof identity claims and bypass authorization checks on protected routes.

Is CVE-2026-54763 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available, though the attack technique is straightforward and should be treated with urgency.

What versions of Traefik are affected by CVE-2026-54763?

Traefik versions 3.7.0 through 3.7.5 are vulnerable. The v2.11.x and v3.6.x branches have corresponding affected versions that are patched in v2.11.51 and v3.6.22 respectively.

How do I check if my server is vulnerable to CVE-2026-54763?

Run 'traefik version' and compare the version number against 3.7.6. If the version is 3.7.5 or lower and you have any auth middleware enabled, your deployment is vulnerable until patched.

Does Defensia detect CVE-2026-54763?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-54763 will appear in your dashboard with remediation steps.

Related Traefik CVEs

CVE-2026-53622CVSS 10Traefik is an HTTP reverse proxy and load balancer. Versions prior to 3.7.3, 3.6.18, and 2.11.51 have a critical vulnerability in Traefik's HTTP/3 (QUIC) TLS configuration selection that allows unauthenticated clients to bypass router-specific mTLS enforcement. When HTTP/3 is enabled on an entrypoint, the TLS handshake selects the applicable TLS configuration through an exact, case-sensitive lookup on the SNI value, which fails to match wildcard host patterns (e.g., *.example.com) or case variants of the configured hostname. Because the handshake falls back to the default TLS configuration — which may not require client certificates — a client can complete the QUIC handshake without presenting a certificate, while the subsequent HTTP routing layer still dispatches the request to a backend protected by a router-specific mTLS policy. The issue affects deployments where HTTP/3 is enabled, a router uses a wildcard Host rule or case-insensitive hostname matching, a router-specific TLSOptions enforces client certificate authentication, and UDP access to the entrypoint is reachable by an attacker. This vulnerability is fixed in versions 3.7.3, 3.6.18, and 2.11.51.
CVE-2026-48491CVSS 10Traefik is an HTTP reverse proxy and load balancer. From 3.7.0 until 3.7.3, there is a high severity vulnerability in Traefik's domain-fronting protection (SNICheck) that allows an unauthenticated client to bypass mutual TLS enforced through wildcard router TLSOptions. When a router uses a wildcard host rule such as Host(*.example.com) with stricter TLS options (for example RequireAndVerifyClientCert), SNICheck resolves the TLS options for the HTTP Host header using exact map lookups only and never applies wildcard matching. If another permissive SNI is served on the same entrypoint, an attacker can complete the TLS handshake under the permissive options and then send an HTTP Host header targeting the wildcard-protected backend, reaching it without presenting a client certificate. This affects the regular HTTPS / HTTP-2 path and does not require HTTP/3. This vulnerability is fixed in 3.7.3.
CVE-2026-48020CVSS 10Traefik is an HTTP reverse proxy and load balancer. Prior to 2.11.48, 3.6.19, and 3.7.3, there is a high severity vulnerability in Traefik's StripPrefix middleware that allows an unauthenticated attacker to bypass route-level authentication and authorization. When a public router matches on a PathPrefix rule and applies the StripPrefix middleware, a request path containing .. or its percent-encoded form %2e%2e can match the public route at routing time and then, after the prefix is stripped and the path is normalized, resolve to a path served by a separate, authenticated router. As a result, an attacker can reach protected backend paths — such as admin or internal configuration endpoints — without satisfying the authentication middleware attached to the protected router. This vulnerability is fixed in 2.11.48, 3.6.19, and 3.7.3.
CVE-2026-44774CVSS 9.9Traefik is an HTTP reverse proxy and load balancer. Prior to 2.11.46, 3.6.17, and 3.7.1, Traefik's Kubernetes Gateway API provider allows a tenant with HTTPRoute creation permissions to expose the REST provider handler, bypassing the providers.rest.insecure=false setting. The Gateway provider accepts any TraefikService backend reference whose name ends with @internal, making it possible to route traffic to rest@internal in addition to the intended api@internal. In shared Gateway deployments where the REST provider is enabled, this allows a low-privileged actor to gain live dynamic configuration write access to Traefik, enabling unauthorized reconfiguration of routers and services. This vulnerability is fixed in 2.11.46, 3.6.17, and 3.7.1.
CVE-2026-88877CVSS 9.8Traefik is a HTTP reverse proxy and load balancer. In versions >= v3.7.0 and <= v3.7.11, the Kubernetes ingress-nginx provider mishandles Ingresses that carry both an authentication annotation and the nginx.ingress.kubernetes.io/from-to-www-redirect annotation. For such Ingresses the provider creates an additional 'sibling' router that matches on the host alone, carries only the RedirectRegex middleware, and still points at the parent router's protected backend service. Because RedirectRegex is not a terminal handler, a request its pattern does not match is forwarded to the backend, and because the redirect pattern only accepts a numeric port while Traefik's host matcher canonicalizes the authority via net.SplitHostPort, a request with a non-numeric or empty port (for example 'Host: www.example.com:x') selects the sibling router, misses the redirect, and is proxied to the protected backend with none of the Ingress's annotation-derived middlewares applied. This discards not only authentication (e.g. BasicAuth) but every annotation-derived middleware, including source-IP allowlisting. Traefik v2 and v3 releases before v3.7.0 are not affected. The issue is fixed in v3.7.12.

References

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